Multicomponent Adsorption Isotherms Research Articles

Engineering Insights into Tailored Metal-Organic Frameworks for CO2 Capture in Industrial Processes.

Despite the known impacts on climate change of carbon dioxide emissions, the continued use of fossil fuels for energy generation leading to the emission of carbon dioxide (CO2) into the atmosphere is evident. Therefore, innovation to address and reduce CO2 emissions from industrial operations remains an urgent and crucial priority. A viable strategy in the area is postcombustion capture mainly through absorption by aqueous alkanolamines, which focuses on the separation of CO2 from flue gas, despite its limitations. Within this context, porous materials, particularly metal-organic frameworks (MOFs), have arisen as favorable alternatives owing to their significant adsorption capacity, selectivity, and reduced regeneration energy demands. This research evaluates the engineering insights into tailored MOFs for enhanced CO2 capture, focusing on three series of MOFs (ZIF, UiO-66, and BTC) to investigate the effects of organic ligands, functional groups, and metal ions. The evaluation encompassed a range of aspects including adsorption isotherms of pure gases [CO2 and nitrogen (N2)] and mixed gas mixture (CO2 and N2 with 15:85% ratio), along with utilization of the ideal adsorbed solution theory (IAST) to simulate multicomponent gas adsorption isotherms. Moreover, the reliability of IAST for mixed gas adsorption prediction has been investigated in detail. The research offers valuable insights into the correlation between the characteristics of MOFs and their effectiveness in gas separation and how these characteristics contribute to the differences between IAST predictions and experimental results. The findings enhance the understanding of how to enhance MOF characteristics in order to reduce CO2 emissions and also highlight the need for advanced models that consider thermodynamic nonidealities to accurately predict the behavior of mixed gas adsorption in MOFs. As a result, the incorporation of MOFs with enhanced predictability and reliability into CO2 capture industrial processes is facilitated.

Development of a Multicomponent Adsorption Isotherm Equation and Its Validation by Modeling.

Researchers have made significant efforts over the past few decades to understand adsorption by developing various simple adsorption isotherm models. However, though many contaminants usually occur as multicomponent mixtures in nature, multicomponent adsorption isotherms have received limited attention and remain an area of inadequate research. We have presented here in a new multicomponent adsorption isotherm model, named the Jeppu Amrutha Manipal Multicomponent (JAMM) isotherm, that can alleviate this problem. We first developed the JAMM multicomponent isotherm using our experimental data sets of arsenic and fluoride competitive adsorption on activated carbon. We then tested the JAMM multicomponent isotherm for a case study of cadmium and zinc competitive adsorption. Next, we further assessed the JAMM isotherm using another competitive adsorption case study of copper and chromium. Through extensive validation studies and error analysis, the JAMM isotherm was able to demonstrate its efficacy in predicting the adsorption behavior in several multicomponent adsorption systems accurately. The main advantage of JAMM isotherm over other multicomponent isotherms is that it utilizes and leverages the single-component adsorption parameters to simulate multicomponent isotherms. The proposed JAMM analytical isotherm model furthermore incorporates the interaction between the components, a mole fraction parameter, and a heterogeneity index, providing a more comprehensive modeling framework for multicomponent adsorption. The mole fraction term was introduced for the distribution of adsorption sites based on the relative number of molecules of each component. An additional term for interaction coefficient was introduced for the representation of interactions. During the validation of JAMM with three experimental case studies with negligible, small, and high competition systems of adsorbates, impressive predictions were exhibited, with the average normalized absolute percentage error as 6.05% and average R2 as 0.86, highlighting the model's robustness, versatility, and reliability. We propose that the new JAMM isotherm modeling framework might profoundly help in chemical engineering, environmental engineering, and materials science applications by providing a potent tool for analyzing and predicting multicomponent adsorption systems.

Mitigation of arsenic and fluoride from water via porous polymeric network knitted with zirconium moiety in three-dimensional shape: Experimental and mathematical modeling investigation

The presence of toxic contaminants in water seriously threatens human health. Thus, in order to address the water pollution through toxic contaminants, a new type of cross-linked porous polymeric microsphere namely; poly(Zirconyl dimethacrylate) (pZrDMA), was successfully prepared by a single-step facile approach. The pZrDMA comprises an acrylate chain of zirconium moiety, which is a proficient adsorbent for arsenic and fluoride remediation. A series of pZrDMA were prepared by varying the relative amounts of reactants to get an appropriate composition. The pZrDMA having, a high surface area (SA: 392.12 m2 g−1) and porosity (Pore size: 0.93–2.36 µm), has exhibited maximum adsorption capacities (qe) of 4.26 mg g−1, 4.22 mg g−1 and 198.5 mg g−1 As(V), As(III) and F− respectively. The pZrDMA displayed high removal efficiency (>97 %) for all the ions over a wide pH range (2.0 ± 0.2 to 10 ± 0.2). The adsorption kinetic and isotherms are well described by the pseudo-second-order model (PSO), and Langmuir isotherm model for both toxic ions arsenic and fluoride. The multicomponent adsorption isotherm with arsenic and fluoride has also studied. The experimental data analysis using the ANN model provides a high accuracy of the model with larger correlation coefficient values (R > 0.99). The pore diffusion modeling predicted the breakthrough time of 174 h, 1542 h, and 1466 h for F−, As(V), and As (III), respectively.

Genetic algorithm optimized artificial neural network models of single- and multi-component gas adsorption isotherms for hydrogen purification

Accurate isotherm models contribute to predicting the amount of adsorbate adsorbed in the adsorbent within a certain range of pressure and temperature. Experimental adsorption isotherms of five components (CO2, CO, N2, CH4 and H2) on pelletized zeolite 13X from publication data were correlated with common-used fundamental isotherm models, including Langmuir, Sips, dual-site Langmuir (DSL), and temperature-dependent (TD) isotherm models, including TD Langmuir, TD Sips and TD DSL. Overall, the average relative errors (AREs) of TD models are higher than those of common-used fundamental isotherm models, but TD models have better applicability. In addition, three surrogate artificial neural networks (ANNs) optimized by genetic algorithm (GA) of single- and multi-component gas adsorption isotherm models are proposed. Three GA-ANN models set the adsorption amount as the output and take one, two or three potential inputs, such as adsorption pressure, temperature and adsorbate components. Three GA-ANN models generally have lower AREs and better applicability than fundamental isotherm models and TD isotherm models. The proposed GA-ANN3 model, which has three inputs, makes a new attempt at adsorption isotherms and can fit the multi-component gas adsorption at different temperatures with the change of adsorption pressure. The adsorber dynamics for multi-component adsorption (CO2: CO: N2: H2 = 19.9: 0.1: 44.6: 35.4 mol%) in zeolite 13X bed are compared by the extended TD Langmuir model and extended TD DSL model. Since the AREs of the TD DSL model are smaller than that of the TD Langmuir, the breakthrough curves of multi-component gas simulated by the TD DSL model are better than that of TD Langmuir. These results can contribute to relevant researchers choosing suitable adsorption isotherm models for numerical simulations of adsorption processes.

Multi-component Adsorption Isotherms: Review and Modeling Studies

Adsorption is an important phenomenon widely used for the removal of contaminants. Several drinking water contaminants such as arsenic and fluoride, vanadium and chromium, nickel, cadmium and cobalt are found to coexist in nature as multi-component mixtures in water. Hence, the modeling of multi-component adsorption isotherms for designing water treatment systems has gained importance recently. However, review studies of multi-component adsorption and competitive adsorption modeling are limited. The current review paper summarizes twenty-six multi-component adsorption isotherm models. Also, case studies of several common multi-component adsorption systems and the mechanisms of multi-component adsorption are discussed. Furthermore, a modeling analysis of four multi-component isotherms models for three commonly found two-component adsorption systems, i.e., cadmium-nickel, nickel–cobalt, and cadmium-cobalt, is reported. The Extended Langmuir isotherm, Competitive Langmuir isotherm, Extended Langmuir–Freundlich isotherm and Extended Freundlich isotherm models were applied in the modeling study for the competitive adsorption of Cd, Ni, and Co. The goodness of fit parameters and adsorption isotherm constants were estimated for these models. The factors influencing competitive adsorption, mechanisms of adsorption, various single and multi-component isotherm models, their significance, and limitations are also discussed in this review article.Highlights• Twenty-six multi-component and ten single-component isotherm models are compiled• Factors affecting multi-component competitive adsorption isotherms are discussed in this review paper• The applications of four multi-component isotherm models for three binary contaminant systems are presented.Graphical

How Important Is the Internal Hydrophobicity of Metal-Organic Frameworks for the Separation of Water/Alcohol Mixtures?

Short-chain alcohols obtained by fermentation will play a key role in the industrial transformation toward green chemistry because of their use as fuel additives and fuels or for their conversion into olefins. The fermentation broth is often a highly diluted aqueous solution that requires separation, for instance, by liquid phase adsorption in nanoporous materials. However, entropy effects that prefer the adsorption of water might significantly reduce the separation efficiency─even in nanoporous materials with internal hydrophobicity. In this paper, we investigate this assumption by a case study on the separation of aqueous alcohol mixtures by liquid phase adsorption in CAU-10─an ultramicroporous metal-organic framework with internal hydrophobicity─using adsorption experiments and grand canonical Monte Carlo simulations to predict both the unary gas adsorption isotherms of ethanol, n-butanol, or water as well as the multicomponent liquid phase adsorption isotherms of their mixtures. It was observed that separation from the liquid phase is commonly driven by entropy effects and strong interactions between the guest molecules─both favoring the adsorption of water and thus complicating the separation of fermentation product by adsorption─while the internal hydrophobicity of CAU-10 is of comparatively little importance.

Analysis of non competitive and competitive adsorption behaviour of ciprofloxacin hydrochloride and ofloxacin hydrochloride from aqueous solution using oryza sativa husk ash (single and binary adsorption of antibiotics)

Among various pharmaceutical pollutants, broad spectrum antibiotics of fluoroquinolones family, emerged as major water contaminants, usually occur in the form of multicomponent mixtures in the aquatic environment. Present study pertains to the adsorption of ciprofloxacin hydrochloride and ofloxacin hydrochloride as pure component and binary mixtures under dynamic and equilibrium conditions using oryza sativa husk ash as adsorbent and characterized using XRD, FTIR and SEM analyses. Single batch adsorption was carried out to study the dependence of drug concentration, time, pH and temperature and the process was found to be dependent on all the parameters investigated, with a pH of 8 for optimum removal of both drugs at which binary adsorption of [ciplox + oflox] and [oflox + ciplox] mixture was carried out for concentration ratios 1:0, 1:0.5, 1:1, 1:1.5, 1:2 to validate the effect of presence of each on the uptake of other. Applicability of Langmuir multicomponent adsorption isotherm revealed that the affinity of each drug was depressed by the presence of other; hence the effect of the mixtures seemed to be antagonistic. Also the present study highlights the oryza sativa husk ash as a viable, cost-effective and efficient bioadsorbent for the removal of antibiotics from multicomponent mixtures, specifically for small scale industries.

Fracture-Matrix Modeling Technique Unlocks CO2 Enhanced Shale Gas Recovery

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202222, “Fracture-Matrix Modeling of CO2 Enhanced Shale Gas Recovery in Compressible Shale,” by Dhruvit Satishchandra Berawala, SPE, Equinor, and Pål Østebø Andersen, University of Stavanger. The paper has not been peer reviewed. With technology available at the time of writing, only 3–10% of gas from tight shale is recovered economically through natural depletion, demonstrating a significant potential for enhanced shale gas recovery (ESGR). Experimental studies have demonstrated that shale kerogen/organic matter has a higher adsorption affinity for carbon dioxide (CO2) than methane (CH4). CO2 is preferentially adsorbed over CH4 with a ratio of as much as 5:1. The complete paper examines CO2 ESGR in compressible shale during huff ’n’ puff injection to understand better the parameters controlling its feasibility and effectiveness. The authors present a mathematical model in the complete paper in which the CO2/CH4 substitution mechanism is implemented in an injection/production setting representative of field implementation. Introduction Modeling of CO2 injection and the interplay between CO2 and CH4 sorption has been extremely challenging for scientists and engineers. The presence of CO2 with methane during the CO2 ESGR process makes gas-desorption behavior and measurement more difficult. Few researchers have evaluated the efficiency of CO2 ESGR in compressible shale. To improve the understanding of this technique, the authors present a numerical modeling approach using a 1D+1D fracture-matrix model in order to study the feasibility of CO2 injection in shale formations. The model consists of a high-permeability fracture extending from a well perforation, symmetrically surrounded by a shale matrix as shown in Fig. 1 of the complete paper. The fracture is assumed to have fixed width for simplicity. The system is assumed to consist of free gas in the pores as well as adsorbed gas in the matrix. When pressure in the well is reduced, free and adsorbed gas from the matrix flows toward the fracture and then to the well. The pressure-based advective forces, along with concentration-based diffusive forces, are considered the main transport mechanisms in this work. After the CH4 production cycle, CO2 is injected from the same well into the fracture and to the matrix. Injection of CO2 leads to an increase in total gas pressure in the system. CH4/CO2 adsorption kinetics are modeled using a multicomponent adsorption isotherm presented in earlier works by the authors. Apparent permeability is used to account for gas slippage effect, effective stress, adsorption, and other flow regimes relevant to the nanopore structure of the shale formation. The effect that compressible rock has on the porosity and apparent permeability changes with CH4 production. CO2 injection also is considered. The resulting model is composed of nonlinear partial differential equations that are solved numerically using an operator splitting approach. The geometry, mole conservation, pressure-dependent parameters, and initial and boundary conditions of the mathematical model are detailed in the complete paper, including mathematical definitions and solution procedures in its appendix.

Use of Microfluidic Capillary Electrophoresis for the Determination of Multi-Component Protein Adsorption Isotherms: Application to High-Throughput Analysis for Hydrophobic Interaction Chromatography.

Chromatography is a widely used separation process for purification of biopharmaceuticals that is able to obtain high purities and concentrations. The phenomena that occur during separation, mass transfer and adsorption are quite complex. To better understand these phenomena and their mechanisms, multi-component adsorption isotherms must be investigated. High-throughput methodologies are a very powerful tool to determine adsorption isotherms and they waste very small amounts of sample and chemicals, but the quantification of component concentrations is a real bottleneck in multi-component isotherm determination. The behavior of bovine serum albumin, Corynebacterium diphtheriae CRM197 protein and lysozyme, selected as model proteins in binary mixtures with hydrophobic resin, is investigated here. In this work we propose a new method for determining multi-component adsorption isotherms using high-throughput experiments with filter plates, by exploiting microfluidic capillary electrophoresis. The precision and accuracy of the microfluidic capillary electrophoresis platform were evaluated in order to assess the procedure; they were both found to be high and the procedure is thus reliable in determining adsorption isotherms for binary mixtures. Multi-component adsorption isotherms were determined with a totally high-throughput procedure that turned out to be a very fast and powerful tool. The same procedure can be applied to every kind of high-throughput screening.

Molecular sieving of linear and branched C6 alkanes by tannin-derived carbons

Two micro-mesoporous carbons (MMCs): a disordered mesoporous carbon (DMC) and an ordered mesoporous carbon (OMC), synthesized by an easy, low-cost, and green method are proposed as efficient hydrocarbon sieves for the separation of C6 isomers: n-hexane (nHEX), 2-methylpenthane (2 MP) and 2,2-dimethylbutane (22DMB). Their textural characterization reveals a highly interconnected pore network within the DMC, while a reverse hierarchy of ordered mesopores only accessible through narrow micropores is found in the OMC. The pore texture strongly affects their adsorption performance by kinetic and molecular sieving effects; the narrow constrictions in the OMC allow adsorption of nHEX and partially 2 MP but not 22DMB, whereas the highly connected pore network of DMC allows adsorption of the three isomers. Multi-component adsorption isotherms calculated from the single-component experimental results by ideal adsorbed solution theory (IAST) demonstrates that the OMC material has a remarkably high selectivity for the adsorption of nHEX and nHEX + 2 MP from binary and ternary mixtures, respectively. To the best of the authors’ knowledge, such behavior has never been reported so far for carbon materials. Hence, this study shows that tannin-derived MMCs have great potential to be used as an eco-friendly and low-cost alternative for the selective separation of di-branched C6 isomers.

Evaluation of Multicomponent Adsorption Kinetics for Carbon Dioxide Enhanced Gas Recovery from Tight Shales

SummaryOnly 3 to 10% of gas from tight shale is recovered economically through natural depletion, demonstrating a significant potential for enhanced shale-gas recovery (ESGR). Experimental studies have demonstrated that shale kerogen/organic matter has higher affinity for carbon dioxide (CO2) than methane (CH4), which opens possibilities for carbon storage and new production strategies.This paper presents a new multicomponent adsorption isotherm that is coupled with a flow model for the evaluation of injection/production scenarios. The isotherm is dependent on the assumption that different gas species compete to adsorb on a limited specific surface area. Rather than assuming a capacity of a fixed number of sites or moles, this finite surface area is filled with species taking different amounts of space per mole. The final form is a generalized multicomponent Langmuir isotherm. Experimental adsorption data for CO2 and CH4 on Marcellus Shale are matched with the proposed isotherm using relevant fitting parameters. The isotherm is first applied in static examples to calculate gas-in-place reserves, recovery factors (RFs), and enhanced gas-recovery (EGR) potential according to the contributions from free-gas and adsorbed-gas components. The isotherm is further coupled with a dynamic flow model with application to CO2/CH4 substitution for CO2-ESGR, assuming only a gas phase exists in the system. We study the feasibility and effectiveness of CO2 injection in tight shale formations in an injection/production setting representative of laboratory and field implementation and compare that with regular pressure depletion.The production scenario we consider is a 1D shale-core or matrix system first saturated with free and adsorbed CH4 gas with only the left-side (well) boundary open. During primary depletion, gas is produced from the shale to the well by advection and desorption. This process tends to give low recovery and is entirely dependent on the well pressure. Stopping production and then injecting CO2 into the shale leads to an increase in pressure, where CO2 is preferentially adsorbed over CH4. The injected CO2 displaces but also mixes with the in-situ CH4. Restarting production from the well then allows CH4 gas to be produced in the gas mixture. Diffusion allows the CO2 to travel farther into the matrix while keeping CH4 accessible to the well. Surface substitution further reduces the CO2 content and increases the CH4 content in the gas mixture that is produced to the well. A result of the isotherm and its application of Marcellus experimental data is that adsorption of CO2 with resulting desorption of CH4 will lead to a reduction in total pressure if the CO2 content in the gas composition is increased. That is in itself an important drive mechanism because the pressure gradient driving fluid flow is maintained (pressure buildup is avoided). This is because CO2 takes approximately 24 times less space per mole than CH4.

MODELING OF A RECTANGULAR CHANNEL MONOLITH REACTOR FOR SORPTION-ENHANCED WATER-GAS SHIFT

As CO2 concentration levels in the atmosphere are steadily reaching a point of no return, it is paramount that actions are taken towards mitigating emissions by improving the efficiency of existing processes. Sorption-enhanced water-gas shift (SEWGS) combines the water-gas shift reaction with in-situ adsorption of CO2 on potassium-promoted hydrotalcite (K-HTC). This enables a direct conversion of syngas into separate hot streams of H2 at feed pressure and CO2 at regeneration pressure, making the process attractive for pre-combustion carbon capture and storage (CCS) and reduction of greenhouse gas emissions. The current work is evaluating the high-temperature, high-pressure adsorption step of the SEWGS process enhanced by a novel technology which replaces common packed bed reactors with 3D-printed monolithic structures. This approach would enable an overall increase in process productivity. To this extent, innovative dynamic models based on validated competitive adsorption isotherms were developed in this work. COMSOL Multiphysics was used to develop a 1D computational fluid dynamics (CFD) model of adsorption for a fixed bed reactor in order to verify the model accuracy against existing studies. Subsequently, 2D CFD simulations were developed to describe adsorption inside monolith structures, both free and porous regions. The multi-component adsorption isotherm used in the simulations was validated with published breakthrough capacities for CO2 and H2O at different pressures. Model predictions are in agreement with expected behavior, as monolith reactors provide a more efficient mass transfer, and will be used to enhance the performance of experimental monolith structures used in SEWGS.

Adsorption of phenolic contaminants from water on activated carbon: An insight into single and multicomponent adsorption isotherms

AbstractThe study focuses on the single and multicomponent adsorption of phenolic compounds from solution onto an activated carbon in the concentration range of 50–500 ppm at room temperature. The observed adsorption isotherms were correlated using various predictive and nonpredictive single and multicomponent adsorption isotherm equations. A strong influence of interadsorbate repulsion was evident based on the model proposed using Nitta's adsorption isotherm model.

A model to predict adsorption of mixtures coupled with SAFT-VR Mie Equation of state

We extend the Statistical Associating Fluid Theory for a Mie potential with a Variable Range (SAFT-VR Mie) equation of state for the prediction of multicomponent adsorption isotherms. A generalization for adsorbed mixtures of the model proposed by Franco et al. (Langmuir, 33, 11291–11298, 2017) is obtained through the derivation of the Helmholtz free energy contribution due to the interaction between the fluid mixture and the wall, which is considered as a square-well potential. The resulting model is completely predictive for mixtures and takes into account the pore size and geometry, and the wall-fluid interaction parameters. These parameters are calculated with combining rules using the pure component wall-fluid interaction parameters. The proposed model is applied to different systems: binary mixtures of methane, ethane, ethylene, and propane adsorbed in a carbon molecular sieve, nitrogen and methane on a Metal-Organic Framework (MOF), and a ternary mixture of methane, nitrogen, and hydrogen adsorbed in activated carbon. The predicted adsorption isotherms match the experimental data reasonably well, proving that the theoretical framework on which the proposed model is based comprises a promising and adequate strategy.

110th Anniversary: Comments on Heterogeneity of Practical Adsorbents

Most micro–mesoporous adsorbents used in practical adsorptive fluid (gas and liquid) separation processes are energetically heterogeneous. The adsorbent heterogeneity plays a significant role in establishing the shapes of the equilibrium adsorption isotherms (pure component or mixture), the corresponding heats of adsorption, and the adsorbate mass-transfer rates, which in turn determine the overall separation performance by a process. The sources of the adsorbent heterogeneity are discussed, and the pros and cons of several analytical heterogeneous models describing pure and multicomponent adsorption isotherms, heats, and adsorbate mass-transfer coefficients are analyzed. Several critical effects of the adsorbent heterogeneity on the equilibrium isotherms are presented with examples to describe the complexity of the subject. The overall effect of adsorbent heterogeneity on an adsorptive process performance will, of course, depend on the specific adsorbate–adsorbent–process design combination. The results ...

A New Approach in Predicting Gas Adsorption Isotherms and Isosteric Heats Based on Two-Dimensional Equations of State

The present study provides a modified approach in determining gas adsorption equilibria based on two-dimensional equations of state (2-D EOS). The proposed model utilizes temperature-dependent parameters in the general form of the 2-D EOS. These parameters were considered similar to other well-known isotherm models, such as Langmuir as specifics function of temperature. The proposed model was examined against various experimental single- and multi-component adsorption isotherm data. In most of the investigated cases, the proposed model reduces the error of predictions compared with temperature-independent two-dimensional equations of state. Moreover, utilizing temperature-dependent two-dimensional equations of state, isosteric heat of adsorption was theoretically obtained and compared with experimental heats of adsorption for different homogeneous and heterogeneous adsorption systems. Applying temperature-dependent parameters within 2-D EOS enables us to describe the heterogeneity of considered adsorption systems quite well. Predicted isosteric heats are in good accordance with the experimental data.

Modeling the Effect of Relative Humidity on Adsorption Dynamics of Volatile Organic Compound onto Activated Carbon.

A two-dimensional heterogeneous mathematical model was developed and validated to study the effect of relative humidity on volatile organic compound (VOC) adsorption onto activated carbon. The dynamic adsorption model consists of the macroscopic mass, momentum, and energy conservation equations and includes a multicomponent adsorption isotherm to predict the competitive adsorption equilibria between VOC and water vapor, which is described by an extended Manes method. Experimental verifications show that the model predicted the breakthrough profiles during competitive adsorption of the studied VOCs (2-propanol, acetone, n-butanol, toluene, 1,2,4-trimethylbenzene) at relative humidity range 0-95% with an overall mean relative absolute error (MRAE) of 11.8% for dry (0% RH) conditions and 17.2% for humid (55 and 95% RH) conditions, and normalized root-mean-square error (NRMSE) of 5.5 and 8.4% for dry and humid conditions, respectively. Sensitivity analysis was also conducted to test the robustness of the model in accounting for the impact of relative humidity on VOC adsorption by varying the adsorption temperature. Good agreement was observed between the experimental and simulated results with an overall MRAE of 12.4 and 7.1% for the breakthrough profiles and adsorption capacity, respectively. The model can be used to quantify the impact of carrier gas relative humidity during adsorption of contaminants from gas streams, which is useful when optimizing adsorber design and operating conditions.

Quantification and isotherm modelling of competitive phosphate and silicate adsorption onto micro-sized granular ferric hydroxide.

Adsorption onto ferric hydroxide is a known method to reach very low residual phosphate concentrations. Silicate is omnipresent in surface and industrial waters and reduces the adsorption capacity of ferric hydroxides. The present article focusses on the influences of silicate concentration and contact time on the adsorption of phosphate to a micro-sized iron hydroxide adsorbent (μGFH) and fits adsorption data to multi-component adsorption isotherms. In Berlin drinking water (DOC of approx. 4 mg L−1) at pH 7.0, loadings of 24 mg g−1 P (with 3 mg L−1 initial PO43−–P) and 17 mg L−1 Si (with 9 mg L−1 initial Si) were reached. In deionized water, phosphate shows a high percentage of reversible bonds to μGFH while silicate adsorption is not reversible probably due to polymerization. Depending on the initial silicate concentration, phosphate loadings are reduced by 27, 33 and 47% (for equilibrium concentrations of 1.5 mg L−1) for 9, 14 and 22 mg L−1 Si respectively. Out of eight tested multi-component adsorption models, the Extended Freundlich Model Isotherm (EFMI) describes the simultaneous adsorption of phosphate and silicate best. Thus, providing the means to predict and control phosphate removal. Longer contact times of the adsorbent with silicate prior to addition of phosphate reduce phosphate adsorption significantly. Compared to 7 days of contact with silicate (c0 = 10 mg L−1) prior to phosphate (c0 = 3 mg L−1) addition, 28 and 56 days reduce the μGFH capacity for phosphate by 21 and 43%, respectively.

Competitive adsorption equilibrium modeling of volatile organic compound (VOC) and water vapor onto activated carbon

In this study, the Potential theory-based Manes method was used to describe competitive multicomponent adsorption of VOC and water vapor onto activated carbon. The thermodynamically consistent method was extended to water-miscible VOCs using a Raoult’s law-like relation. The method uses as input the pure single-component adsorption isotherms, which were obtained from the modified Dubinin-Radushkevich (MDR) model for VOCs and the Qi-Hay-Rood (QHR) model for water vapor. The MDR model was applicable for the studied VOCs (2-propanol, acetone, n-butanol, toluene, 1,2,4-trimethylbenzene) with an overall r2 value of 0.998. The QHR isotherm provided a good description for water vapor adsorption on activated carbon with 0.999 r2 value. Experimental validation tests revealed that the multicomponent adsorption isotherm model predicted the VOC adsorption capacity during competitive adsorption with water vapor with an overall mean relative absolute error (MRAE) of 1.9% for non-polar VOCs and 5.2% for polar VOCs. These results are encouraging, as they indicate a good agreement between modeled and experimental results. Hence, the model can potentially be integrated with dynamic adsorption models to optimize adsorber design and operation or model adsorption kinetics.

An explicit multicomponent adsorption isotherm model: accounting for the size-effect for components with Langmuir adsorption behavior

The extended Langmuir (EL) model is a popular multicomponent adsorption equilibria model, which can be based on single component Langmuir isotherms fitted on pure component data. Such explicit models are preferred over their implicit counterparts due to a lower computational requirement. An important shortcoming of the EL model is its inability to capture the adsorbate size effect occurring when the saturation capacities of pure component Langmuir isotherms are dissimilar. In contrast, this size effect is captured by the ideal adsorbed solution theory (IAST), which is centered on a set of implicit equations. In this work, we present an explicit multicomponent adsorption model for components with uneven saturation capacities obeying the Langmuir isotherm equation. This model predicts the expected change in selectivity with mixture composition, and even a selectivity reversal at high pressure when the adsorbates have significantly different molecular sizes. The model is extendable to any number of components, reduces to the Langmuir equation for pure components and to the EL equation when all saturation capacities are equal. The newly proposed model can be used to approximate the IAST and upgrade the EL model without introducing new parameters. Especially for binary mixtures, this model (Eqs. 12–14) offers a simple improvement of the EL model in predicting the experimental adsorption of light alkanes on 13X and 5A zeolites. The presented model is also applied to describe phase-changing adsorbents, in combination with the osmotic framework adsorbed solution theory (OFAST).